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In this photo, dated December 15, 1936, A. H. Saxton, NBC Western Division Engineer, explains the workings of one of the KPO transmitter tubes to Alice Tyler of the NBC Plant Department. The water-cooled final amplifier tubes were rated for 100 KW, and cost $1,600 each in 1933! This tube was kept on display at the NBC studios at 111 Sutter Street in San Francisco.